This invention relates, in general, to coupling members for rotating machinery and in particular to a coupling member between a prime mover and a dynamoelectric machine wherein electrical isolation is maintained between the driver and driven shafts and wherein the torque carrying capability of the coupling is enhanced.
Torque transmitting couplings between a prime mover and load normally require only that the bolts connecting the two mating couplings be able to carry the torque transmitted between the coupling members. When the load is a dynamoelectric machine it is desirable to electrically isolate the coupled shafts to avoid the transfer of electrical current between the two shafts which might set up potentially damaging currents in the prime mover bearing supports and oil seal surfaces. One such coupling is shown in U.S. Pat. No. 4,083,639 to Terry incorporated herein by reference and assigned to the assignee of the present invention.
A limiting factor in the torque carrying capability of an electrically insulated coupling is the strength of the electrical insulation. For example, the mechanical strength of electrical insulation in the coupling described may be only about a third of the yield strength of a metal bolt. Referring to the aforementioned U.S. Patent to Terry, the coupling members are joined at a radial interface which includes a washer which may be formed from an insulation material. The area across which the coupling torque is transmitted is equal to the number of bolts multiplied by the washer thickness and bolt diameter. A further aggravating factor of the prior art radial interface design is that transmitted forces are in shear whereas electrical insulation is more capable of withstanding compression forces.
The present invention improves upon the torque transmitting capability of a coupling by providing a circumferential interface between inner and outer hubs which distributes the torque along the entire length of the insulation wrapped around a plurality of coupling keys. Moreover the force is applied in compression rather than shear.